The invention relates to a beam shaping method.
In the embodiments of the beam shaping method described in this application, covariance matrices are calculated singly for all sufficiently strong taps of a radio signal, eigenvectors and eigenvalues of the covariance matrices thus obtained are calculated and the eigenvectors corresponding to the strongest eigenvalues are used for the beam shaping.
The number of eigenvalues which can be used in practice in the beam shaping is limited. There are different types of reasons for this.
In a method as described with reference to FIG. 4 of patent application DE 10032426.6, a problem lies in the limited bandwidth which is available for transmitting information describing the receiving situation back from the subscriber station to the base station and which must be divided into the transmission of components of the measured eigenvectors, which are valid or usable over relatively long periods, on the one hand, and on the other hand, a desired short-term weighting of these eigenvectors in the downlink signal. This makes it necessary to restrict oneself to the transmission of only the most important eigenvectors in the interest of rapid updating of the weighting.
In the method described with reference to FIG. 5 of patent application DE 10032426.6, the base station uses a linear combination of eigenvectors as weighting vectors for radiating. A greater number of eigenvectors used the greater the number of propagation paths covered with the radio signal, both to the subscriber station for which the signal is intended and to other stations for which the signal represents interference. To keep this interference within limits, the number of eigenvectors included in the linear combination must be limited.